This invention relates to sputtering targets and a method of preparing the same. More particularly, this invention relates to a sputtering target of terbium-iron-cobalt alloy having a uniform homogeneous structure free of cracks.
In the preparation of magnetooptical recording media, sputtering is an important procedure for depositing the magnetooptic media onto a substrate or other layer employed in the recording element. Terbium-iron-cobalt alloys are known to exhibit magnetooptic effect and therefore are important from this standpoint. U.S. Pat. No. 4,670,353, discloses and claims a terbium-iron-cobalt magnetooptical recording media.
It is desirable to prepare magnetooptic elements in a high throughput industrial apparatus. In addition to controlled processing parameters, it is essential that the sputtering targets have a uniform composition and structure. To achieve this goal, highly sophisticated techniques for preparing sputtering targets are available. Such techniques are not practical from a commercial standpoint where large quantities of thermo-magnetooptic elements are to be produced because of the economics involved.
Two apparently suitable techniques for preparing sputtering targets are by hot pressing and casting from the melt. Hot pressed targets, because of the presence of surface oxide in the starting powders, contain large quantities of oxygen. Targets prepared by casting contain low levels of oxygen which is desirable. However, the preparation of quality targets by this method, especially of terbium-iron-cobalt alloy, is extremely difficult, because the cast targets exhibit cracks, voids, defects and other non-uniformities such as, large grain size. These defects result, upon sputtering, in magnetooptic films with low compositional uniformity. Additionally, such targets are very brittle and susceptible to breakage or handling. Terbium-iron-cobalt alloy targets also are easily oxidized and disintegrate in atmospheric conditions.